Various micrometer devices are known in the art for performing high precision measurements of workpieces using a handheld mechanism. For example, U.S. Pat. Nos. 1,132,704; 3,849,890; 4,485,556; 4,561,185; and 8,091,251 (referred to herein as the '704, '890, '556, '185 and '251 patents), each of which is hereby incorporated by reference in its entirety, disclose micrometer devices. In particular, modern micrometers such as that disclosed in U.S. Pat. No. 5,495,677 (the '677 patent) comprise a linear digital sensor for determining measurements, rather than relying on accurate micrometer threads in combination with a rotary position sensing device. Using a linear digital sensor eliminates the need to use an extremely accurate drive or fine pitch threads in order to drive the micrometer. For example, the '677 patent uses very coarse drive threads, and the '251 patent copies features of known spring-loaded gauge designs that use no drive threads.
The micrometer designs referred to above allow fast adjustment of the micrometer. However, they lack certain desirable features of traditional fine-pitch thread-driven micrometers. For example, traditional fine-pitch thread-driven micrometers allow for good ergonomic factors and feel for controlling very fine adjustments. One aspect of the ergonomic factors and feel is that such micrometers can be held and operated in one hand, while the other hand is free to hold the workpiece. In one common technique, the micrometer frame is gripped or hooked in two or three smaller fingers, with the thumb and index finger extended and used to turn the thimble. The fine pitch thread allows good control and stability of the adjustments in this position, whereas most “fast adjustment micrometer” designs such as those referenced above offer somewhat less certain control and/or stability. Another aspect of the ergonomic factors and feel associated with fine-pitch thread-driven micrometers is the inherent stiffness and/or stability of the spindle position, that allows a user to detect or adjust the amount of measuring force or contact on the workpiece surface by dragging or displacing the workpiece slightly in the measuring gap and sensing the amount of drag or “play” of the workpiece in the measuring gap. Users often gain confidence in a measurement setting in this manner, using subtle movements and tactile feedback, either consciously or unconsciously. Again, most “fast adjustment micrometer” designs such as those referenced above offer somewhat less stiffness, control and/or stability in this regard.
U.S. Pat. No. 809,272, discloses a quick adjustment micrometer that is adjustable in one conventional mode using a fine pitch thread in a split nut. The sections of the split nut are carried on, or formed on, deformable arms that can deflect or open radially to disengage the nut from the fine pitch thread, to allow a sliding “quick adjusting” mode wherein the threads slide axially through the open split nut, to quickly move the spindle. However, such a design offers poor adjustment control in the quick mode. Furthermore, its measurement position shifts when the split nut is locked onto a partially axially-misaligned thread. Furthermore, the user must exercise unusual care during operation, in that due to the variable separation between the split nut and the threads, the micrometer is subject to potential scraping and wear of the precision threads sliding on one another. Thus, in order to provide ergonomic, rapid, and convenient functionality for users, there remains a need for a micrometer that can be used to quickly drive a spindle to a desired position, and that also provides for a high stiffness fine adjustment mode that is easily operated and stable, and other desired features.